The problem of condensation forming on mirrors which are exposed to warm, humid air--e.g. in a bathroom--has proven to be a long-standing inconvenience. Extractor fans, they most commonly employed "remedy", are of little help.
Raising the temperature of the mirror's surface above the dew point will prevent the formation of condensation, and so would eliminate the problem of fogging. Various devices have been proposed for doing this, but none appears to have achieved any significant degree of commercial success. In many cases, the prior devices have been deficient from the standpoint of economy of manufacture: For example, many of the proposed devices have required a specially manufactured mirror glass, whereas others require that the mirror element be mounted in a complex frame structure or other installation.
U.S. Pat. No. 4,665,304 (Spencer) discloses a defogging device which is perhaps closest in general configuration to the present invention, inasmuch as this utilizes a sheet-like electric heating element which is mounted adjacent to the back side of the mirror. Other known devices resemble a simple radiant heating pad mounted to the back of a mirror. Devices of this general type have many advantages over more complicated and bulky systems, but they tend to deliver a very unpleasant shock when touched on the edge, especially by a person who is standing on a damp floor or leaning against a sink adjacent to the mirror. As will be described below, it is part of the present invention that the applicants have discovered and eliminated the unexpected source of this problem.
Accordingly, there exists a need for a device for heating a mirror so as to remove or prevent condensation of thereon, which device may be used with standard, inexpensive plate mirror stock, which is thin and does not interfere with the ordinary methods of installing the mirrors, which is impervious to moisture, and which is inexpensive to manufacture. Moreover, there exists a need for such a device having a construction which obviates the possibility of imparting a shock when touched.